Pumping system with improved jet inducer



' Dec. 29, 1970 PPPPPPPPPPP Ts 3,551,073

72W am United States Patent() U.S. Cl. 417-76 4 Claims ABSTRACT OF THEDISCLOSURE transfer supply fuel at vapor to liquid ratios greater than0.30, thus providing for sustained system pumping operations in theevent of failure of the system boost pump.

BACKGROUND OF THE INVENTION (1) Field of invention This inventionrelates to pumping systems. Particularly the present invention isdirected to fuel pumping systems for gas turbine engines, especiallyaircraft gas turbine engines. More particularly, this invention relatesto a fuel pumping system incorporating improved apparatus fortransferring supply fuel having a high gas to liquid ratio at increasedpressure to the inlet of a positive displacei ment fuel pump.

(2) Description of the prior art Positive displacement pumps, especiallygear-type positive displacement pumps, have been employed for some timeto meet the dry lift and high pressure starting requirements of aircraftgas turbine engine fuel pumping systems. The pressure drop encounteredas the fuel traverses a length of fuel line reduces the total pressureapplied to the fuel and permits free gas to come out of solution. Fluidshaving a high vapor to liquid ratio are generally diillcult to pumpellciently due to the formation of pockets of free gas which inhibitflow.

The problem of controlling the gases liberated in liquids transported inconduits, particularly in fuel lines carrying aviation fuels, utilizedeither the overboard release, the compression or the through pumpingmethod. The overboard release method is to collect the free gas andrelease it overboard. The alternative compression method is to install acompressor in the fuel line to increase the line pressure, therebyredissolving the free gases. The overboard release of free gasesinvolves the venting of the gases to atmosphere which permits therelease of volatile vapors, and in the case of flammable vapor creates asafety hazard. The compression method utilizes an external compressor inwhich the size, weight and power consumption of the compressor make thismethod undesirable from the standpoint of large power losses andincreased weight. The through pumping method utilizing jet inducers haveproven successful, in certain applications, as a method of increasingthe pressure of the supply fluid at the inlet of positive displacementfuel pumps, thereby preventing cavitation. Prior pumping systemapproaches utilizing a jet inducer had been found suitable for handlingsupply fluids with a vapor to liquid ratio up to 0.3, i.e., up to 0.30part of vapor for each part of liquid. However, it was found prior artjet inducers would not transfer 3,551,073 Patented Dec. 29, 1970 supplyfuel having a vapor to liquid ratio of 0.30 or greater unless therecirculated llow comprised a minimum of 68% of the total flow. Fuelpumping systems which formerly utilized the through pumping approach ofthe jet inducer as the most desirable method of increasing the fuel linepressure to thereby redissolve liberated free gases were found to be nolonger operationally or economically adequate to deal with the fuelpumping problems presented by the increased vapor to liquid ratio.

(3) Summary of the invention The liquid fluids utilized in all iluidpumping systems contain partially dissolved gases in their normal state.The amount of gas contained for the saturation level is a function oftemperature and pressure. In the case of aviation fuels utilized inaviation gas turbine engine fuel pumping systems, the solubility of airin the aviation fuel is proportional to the difference between the totalpressure applied to the fuel and the vapor pressure of the fuel. In thecase of aviation gas turbine fuel pumping systems, the fuel linepressure drops reduce the total pressure applied to the fuel and permitfree gas to come out of solution. The formation of pockets of free gasinhibits the flow of the tluid in the fuel line and thereby reduces theefllciency of the pumping system. Jet inducers have proven useful t0increase the pressure above the supply pressure and thereby transmitfuel at an increased pressure to the inlet of the main fuel pump suchthat the formation of free gas pockets is inhibited and pump cavitationis prevented. The jet inducer receives fuel from the fuel supply, mixesthe supply fuel with recirculated high pressure fuel flowing from thejet nozzle to supply an increased volume of fuel at increased pressureto the inlet of the positive displacement pump.

Prior art jet inducers will not transfer supply fuel having a vapor toliquid ratio of 0.30 or greater unless the high pressure recirculatedjet nozzle ilow is an uneconomical and inetllciently high percentage ofthe total output flow. The present invention utilizes a jet inducerhaving a mixing chamber so constructed that supply lfuels having a vaporto liquid ratio greatly in excess of 0.30 can be efficiently transferredthrough the jet inducer to the inlet of a positive displacement pump.

The use of this novel improved jet inducer pump is of particularsignificance in that it permits the more economical and reliable throughpumping compression method to be utilized as the means of increasingfuel line pressure to thereby redissolve liberated free gases.Additionally, the inclusion of the jet inducer in the fuel pumpingsystem between the discharge of the fuel supply boost pump and the inletto the positive displacement pump provides a means whereby a fuel supplyhaving a high vapor to liquid ratio can be transferred to the inlet ofthe positive displacement pump without causing cavitation, even in theevent of a boost pump failure.

Accordingly, one object of the present invention is to provide a novelcompression method of increasing the fuel line pressure of a fuelpumping system to thereby redissolve liberated gases.

Another object of the present invention is to provide a novel liquidpumping system including a jet inducer capa-ble of economically handlingsupply fluids on the order of 0.50 vapor to liquid ratio.

Still another object of the present invention is to provide a lluidpumping system including a novel mixing chamber wherein a supply fluidhaving a vapor to liquid ratio on the order of 0.50 is capable, in theevent of a fuel boost pump failure, of being transferred through the jetinducer to the positive displacement pump.

Still another object of the present invention is to provide a fuelpumping system capable of supplying fuel under pressure to a positivedisplacement pump such that the positive displacement pump will notexperiencecavitation in the event of a failure of the fuel supply systemboost pump.

Other objects and advantages will be apparent and understood from thefollowing detailed description of the drawings wherein like elements arenumbered alike in the several figures.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representationof a fuel pumping system incorporating the present invention.

FIG. 2 is an isometric view illustrating the manner in which the novelmixing cham-ber is incorporated in the jet inducer component of thefluid pumping system.

FIG. 3 is a graphic presentation of the comparative performance of aprior art jet inducer with one including7 the novel features of theinstant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Even though described herein forutilization in an aircraft fuel pumping system, it is to be understoodthat the present invention is applicable to any liquid pump systemincorporating a jet inducer in which the presence of liberated gasresulting from reduced total pressure reduces the operating efficiencyof the pumping system.

Referring now to FIG. 1, fuel from a tank 10 enters a submerged rststage boost pump 14, usually a centrifugal pump, wherein the fuel isconveyed through pump 14 to conduit 16 and thence to jet inducer 18. Theflow of fluid from tank 10 to inducer 18 is indicated by the arrow inconduit 16, and it will be understood that such arrows in any of theconduits of FIG. 1 indicate the direction of fuel flow therein when fuelis flowing in that conduit. The fuel entering jet inducer 18 fromconduit 16 is joined with the fluid entering inducer 18 via conduit 20to provide a total outlet flow that is delivered via conduit 22 to theinlet of positive displacement pump 24. The details of jet inducer 18will be described hereinafter with reference to FIG. 2, but, for thepurposes of the immediate description, it is sufficient to state thatfuel is transferred from the fuel tank 10 to the jet inducer 18 andcombined with the recirculation flow of conduit 20 to provide a totalfiow in conduit 22 at an increased pressure such that a fluid flow of anincreased volume and pressure is delivered to the inlet of positivedisplacement pump 24 to thereby prevent cavitation. The fuel entersboost pump 14 at pump inlet pressure, and exits pump 14 into conduit 16at a higher pressure, referred to as yboost pump pressure. Fuel entersjet inducer 18 at a pressure, referred to as recirculation or drivepressure, and combines with fiuid in conduit 16 at boost pump pressure,and exits in conduit 22 at an increased pressure and flow, referred toas positive displacement pump inlet pressure. Conduit 22 delivers fuelat inlet pressure to the positive displacement pump 24 where thepressure is increased to a level referred to as pump discharge pressure,and the fuel at pump discharge pressure, as indicated by the arrow inconduit 26, is delivered to fuel control 28 where the fuel flow isdivided with a portion proceeding, as indicated by the arrow in conduit30, to the prime mover 32. A second portion, representing the unusedfuel from the fuel control, is recirculated via conduit 20 to the jetinducer 18. It can be seen that the capacity of pump 22 must be greaterthan the maximuml fuel utilization of fuel control 28 such that aby-pass fuel flow will always be available as the recirculation flow inconduit 20 to jet inducer 18. As stated, all liquids contain partiallydissolved gases in their normal state. In the particular instanceillustrated herein, the solubility of air in aviation fuels isproportional to the difference between the total pressure applied to thefuel and the vapor pressure of the fuel. It can be seen that as fuelflows in conduit 16, due to fluid friction, the fuel line pressure dropreduces the total pressure applied to the fuel. This reduction in totalpressure permits free gas to come out of solution. It is obvious thatthe quantity of free gas that comes out of solution is a function of themagnitude of the reduction in total pressure. The vapor to liquid ratio,that is the number of parts of vapor for each part of liquid, is a termutilized to dene the operational limitations and pumping capabilities ofa particular fuel pumping system.

Utilizing aviation fuels in combination with the apparatus shown in FIG.l, with the boost pump 14 inoperative, thereby simulating a boost pumpfailure, the Vapor to liquid ratio of the fluid in conduit 16 isapproximately 0.30. At a vapor to liquid ratio of 0.30, it was foundthat prior art jet inducers would not transfer fuel from conduit 16unless the recirculation ow comprised a minimum of 68% of the totaldischarge flow in conduit 22. A recirculation flow representing 68% ofthe total flow renders the pumping efficiency of such a jet inducersystem economically unacceptable. Thus, the presence of a vapor toliquid ratio of 0.30 at the induction inlet 16 of the jet inducerpresents a pumping system operational and efficiency problem which mustbe solved.

Referring now to FIG. 2, a jet inducer is shown generally at 18.Recirculation fuel at high pressure enters inducer 18 via conduit 20 andpasses through nozzle 34. Nozzle 34 is mounted in a mixing chamber 36having a longitudinally extending interior peripheral wall. The fuelpassing through nozzle 34 is accelerated such that a local reducedpressure is established at the mixing chamber 36 adjacent the throatarea of nozzle 34. This local low pressure increases the pressuregradient between fuel tank 10 and chamber 36, thus providing anincreased motive force to cause fluid to ow from tank 10 via pump 14 andconduit 16 such that an additive force is supplied to that generated byboostpump 14 and additionally furnishes a source of motive force in theevent of a failure of boost pump 14. The local point of low pressureestablished in chamber 36 permits dissolved gas to escape from solutionand form vapor pockets which hinder the flow of fluid through chamber 36to exit port 38 and thence to conduit 22.

It has been found that by increasing the roughness of the surface ofmixing chamber 36, the characteristics of the flow in the area ofchamber 36 for the same range of Reynolds numbers can be changed from alaminar/ turbulent transition flow to a completely turbulent ow withattendant improvements in the pumping performance of the jet inducer.

An increase in the relative roughness of the periphery of mixing chamber36 can be accomplished by several methods, such as rough grinding theperiphery of -the walls of chamber 36, or inserting a Wire mesh screenin contact with the periphery of the mixing chamber wall therebydefining a wall having a knurled surface. It has been found that anincrease in the relative roughness of the .surface of the mixing chambercould be most expeditiously accomplished by the inclusion of a wire meshscreen 40 placed in contact with the wall of mixing chamber 36, as shownin FIG. 2. To illustrate, by completely covering the cylindrical wall ofmixing chamber 36 -with a 20 x 20 x .016 wire mesh screen 40, as shownin FIG. 2, the relative roughness was raised from about .0015 to about.0100, on a Moody diagram well known to those skilled in the art.

It has been found that increasing the relative roughness of the surfaceof mixing chamber 36 causes the flow in mixing chamber 36, representedby the intersection of conduit 16 and nozzle 34, to be transformed froma laminar/turbulent transition flow to an unstratified turbulent fiowsuch that the gas liberated from solution in the mixing chamber area isuniformly disbursed in the fluid, thereby completely preventing theformation of flow hindering vapor pockets and markedly improving theperformance characteristics of the jet inducer.

To better appreciate the increases or improvements realized from thisnovel construction of a jet inducer mixing chamber, it is to be noted inFIG. 3 that in a prior art jet inducer for a vapor to liquid ratio of.3, a 68% recirculation flow is required; whereas, with the improved rjet inducer, represented by the instant invention, only 34%recirculation flow is required for the same total output oW, at the sameReynolds numbers, thus more than doubling the induced flow capability ofthis tluid pumping system. This increased pumping performance permits athrough ow jet inducer to be utilized in a fuel pumping system includinga centrifugal boost pump, wherein the requirements of the system aresuch that the system pumping operation must be sustained in the event ofa boost pump failure.

While a preferred embodiment has been shown and described, variousmodilications and substitutions may be made Without departing from thespirit and scope of this invention. Accordingly, it is to be understoodthat this invention has been described by Way of illustration ratherthan limitation.

What I claim is:

1. A jet inducer comprising:

a housing defining a chamber therein with a longitudinally extendinginterior peripheral wall;

a first inlet conduit for receiving a ow of fluid;

a nozzle mounted in the chamber in fluid communication with the firstinlet conduit for accelerating a flow of uid therefrom and establishinga local reduced pressure adjacent the throat area of the nozzle;

an outlet conduit in uid communication with the chamber and the nozzlefor receiving a ow of uid from the chamber;

a second inlet conduit in fluid communication with the chamber andextending through the wall thereof for receiving a flow of fluid from atank, the ilow therefrom being induced by the local reduced pressureadjacent the throat area of the nozzle;

said interior peripheral wall having a knurled surface which provides arelative wall roughness substantially above .0015 on a Moody diagram,said knurled surface covering a major portion of the wall and being atleast partially located in the circumferential region of the secondinlet conduit; and whereby, the formation of vapor pockets in thechamber is prevented by turbulence generated by the projections. 2. Ajet inducer, as defined in claim 1, wherein the knurled surface isformed by:

a mesh screen secured to the Wall of the chamber, 3. A fuel pumpingsystem incorporating a jet inducer, as defined in claim 1, including:

a boost pump iiuidly connected to the second inlet conduit; and apositive displacement pump tluidly connected to the outlet conduit. 4. Afuel pumping system incorporating a jet inducer as defined in claim 1,including:

a tank in fluid communication with the second inlet conduit for supplyfuel thereto.

References Cited UNITED STATES PATENTS 683,005 9/ 1901 Sewall 103-277X826,355 7/ 1906 Pollard 103-278 972,441 l0/ 1910 Durdin, Ir l03-260973,351 10/1910 Hoffman 103-277 1,692,916 11/1928 Woodruff 103-2622,479,783 8/ 1949 Sawyer et al. 103-262X 2,690,717 10/ 1954 Goodrie10S-262 3,010,232 11/1961 Skakel et al. 103-262X 3,387,644 6/1968Heinecke et al. 103-5(J)UX CARLTON R. CROYLE, Primary Examiner W. I.KRAUSS, Assistant Examiner U.S. Cl. X.R.

